How to fix 'target' must be specified or 'lib' must contain 'dom' in TypeScript

First, examine your tsconfig.json file to see what compiler options are set:

// Look for these fields in your tsconfig.json
{
  "compilerOptions": {
    // Check if "target" exists
    "target": "es2020",
    
    // Check if "lib" exists and includes "dom"
    "lib": ["es2020", "dom"]
  }
}

If either "target" or "lib" is missing, you'll need to add them.

Add a "target" field to your tsconfig.json. For modern web projects, use "es2020" or later:

{
  "compilerOptions": {
    "target": "es2020",
    // ... other options
  }
}

Common target values:
- "es2020" or "es2022": Modern JavaScript features
- "esnext": Latest ECMAScript features
- "es5": Maximum browser compatibility (older browsers)

The "target" setting tells TypeScript which JavaScript version to emit.

If you prefer not to set a target, you can explicitly include "dom" in the lib array:

{
  "compilerOptions": {
    "lib": ["es2020", "dom"],
    // ... other options
  }
}

Common lib combinations:
- ["es2020", "dom"]: Modern ES features + browser APIs
- ["esnext", "dom", "dom.iterable"]: Latest features + DOM iteration
- ["es5", "dom"]: Older browser support

The "dom" library includes TypeScript definitions for browser APIs.

After updating tsconfig.json, test your configuration:

1. Restart your TypeScript server (in VS Code: Command Palette → "TypeScript: Restart TS Server")
2. Run the TypeScript compiler:

npx tsc --noEmit

3. Check if the error disappears
4. Verify DOM APIs are now recognized:

// This should no longer show errors
document.getElementById("app");
window.location.href = "/";
const element: HTMLElement = document.createElement("div");

Node.js projects: If you're building a Node.js backend, use "node" lib instead of "dom":

{
  "compilerOptions": {
    "target": "es2020",
    "lib": ["es2020"],
    "module": "commonjs"
  }
}

Mixed environments: For universal/isomorphic code:

{
  "compilerOptions": {
    "target": "es2020",
    "lib": ["es2020", "dom"]
  }
}

Extending configurations: If using extends, ensure parent config has required options:

{
  "extends": "./base-tsconfig.json",
  "compilerOptions": {
    // Override or add missing options
    "target": "es2020",
    "lib": ["es2020", "dom"]
  }
}